1. Field of the Invention
The present invention relates to a high-frequency oscillation element to be used in a magnetic sensor, as well as to a magnetic information recording head and a magnetic storage device, both pertaining to high-density magnetic recording.
2. Description of the Related Art
Since the inception of a GMR head employing a giant magnetoresistance effect (GMR effect), recording density of magnetic recording has been increased at a rate of about 100% per year. GMR elements include a spin-valve-type element and an artificial-lattice-type element.
The spin-valve-type element has a multilayer film including a ferromagnetic layer/nonmagnetic layer/ferromagnetic layer. The magnetization of one of the ferromagnetic layers is fixed by applying, e.g., an exchange bias magnetic field from an antiferromagnetic film, whereby the magnetization direction of the other ferromagnetic layer is reversed by an external magnetic field (signal magnetic field). Accordingly, a relative angle between magnetization directions of the two ferromagnetic layers changes, and this change can be detected as a change in the element resistance. A GMR element of spin-valve type exhibits a change in magnetic resistance of about 10% and is considered to be able to achieve a recording density of 200 Gbit/inch2 or thereabouts.
To cope with higher-density magnetic recording, TMR elements employing a tunnel magnetoresistance effect (TMR effect) have been developed. A TMR element has a multilayer film including a ferromagnetic layer/tunnel dielectric layer/ferromagnetic layer. When a voltage is applied between the two ferromagnetic layers, a tunnel current flows into the TMR element.
The phenomenon of the magnitude of a tunnel current changing in accordance with the magnetization direction of the two ferromagnetic layers can be utilized in detecting a change in the relative angle between the two ferromagnetic material layers as a change in tunnel resistance. An obtained MR ratio of the TMR element is approximately 50% maximum and can be considered to achieve a recording density of 300 Gbit/inch2.
In addition to the above, an element using spin-polarized current in a ferromagnetic material has been suggested. For example, in a spin injection three-terminal element, a transistor which performs gating by injecting spin-polarized current from a ferromagnetic material electrode into channels has been suggested (see JP-A-2002-26417).
Magnetic recording at 500 Gdpsi or more requires a bit size of about 50 nm or less. Therefore, a medium having large coercive force is used for reducing thermal fluctuations of micro-magnetization. For this reason, at the time of writing of magnetic information, a heat assistance method is employed for simultaneously supplying a magnetic field and heat to a bit area of a medium where the magnetic information is to be recorded. The heat assistance method requires a high-speed characteristic of adapting to travel of a head at a frequency on the order of GHz, as well as requiring heat radiation having a large power density having locality corresponding to a bit area of tens of square nanometers. However, no specific idea has yet been put forth.
The same read/write problem is also found in magnetic random access memory (MRAM), which is one type of solid-state memory. When storage information is written in a memory cell of the MRAM, the information is written through use of a current magnetic field derived from two current lines. However, the MRAM is highly integrated, and it has been pointed out that crosstalk arises in the current magnetic field derived from adjacent current lines, thereby hindering high-speed storage of accurate information in a fine memory cell.